A closed planar quadrilateral with opposite sides of equal lengths and ,

and with four right angles. A square is a degenerate rectangle with a=b

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`The area of the rectangle is A=ab`

and its polygon diagonals p and q are of length

A rectangle has a circumcircle with circumradius

but incircle only in the degenerate case of a square.

Reference : http://mathworld.wolfram.com/Rectangle.html